The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical automatic transmission includes a hydraulic control system that, among other functions, is employed to actuate a plurality of torque transmitting devices. These torque transmitting devices may be, for example, friction clutches and brakes. The conventional hydraulic control system typically includes a main pump that provides a pressurized fluid, such as oil, to a plurality of valves and solenoids within a valve body. The main pump is driven by the engine of the motor vehicle. The valves and solenoids are operable to direct the pressurized hydraulic fluid through a hydraulic fluid circuit to the plurality of torque transmitting devices within the transmission. The pressurized hydraulic fluid delivered to the torque transmitting devices is used to engage or disengage the devices in order to obtain different gear ratios.
In order to increase the fuel economy of motor vehicles, it is desirable to stop the engine during certain circumstances, such as when stopped at a red light or idling. However, during this automatic stop, the pump is no longer driven by the engine. Accordingly, hydraulic fluid pressure within the hydraulic control system drops. This leads to clutches and/or brakes within the transmission to be fully disengaged. As the engine restarts, these clutches and/or brakes may take time to reengage fully, thereby producing slippage and delay between engagement of the accelerator pedal or release of the brake and the movement of the motor vehicle. Additionally, there are conditions where automatically shutting off the engine is not desirable, such as during brief stops or idling while still moving.
Therefore, there is a need in the art for a system and method for controlling automatic engine stop-starts based on motor vehicle operating conditions as well as providing controllability of the motor vehicle during engine restart.